1. Field of the Invention
The present invention relates to nonreciprocal circuit devices for use in microwave bands, such as isolators and circulators, and communication apparatuses including the devices.
2. Description of the Related Art
A nonreciprocal circuit device for use mainly in microwave bands has been used, having a resin housing having input and output terminals and a ground terminal, a central conductor in electric conduction to the input and output terminals and the ground terminal, a ferrite core close to the central conductor, a permanent magnet applying a static magnetic field to the ferrite core, and a terminating resistor provided in the terminating side of the central conductor are provided.
In a nonreciprocal circuit device of the above type, the central conductor has an input port, an output port, and a terminating-side port. Some specifications have been proposed for the uses of the ports. The specifications are described with reference to FIGS. 8A to 8C and 9A to 9C. FIG. 8A shows a nonreciprocal circuit device in which parallel capacitors are connected to all ports. FIG. 8B shows a nonreciprocal circuit device in which parallel capacitors are connected to all ports, and series coils and series capacitors are inserted. FIG. 8C shows a nonreciprocal circuit device in which parallel capacitors are connected to all ports, and series capacitors are inserted.
FIG. 9A shows a nonreciprocal circuit device in which parallel capacitors are connected to all ports, and a series coil and a series capacitor are inserted only in an input port. FIG. 9B shows a nonreciprocal circuit device in which parallel capacitors are connected to all ports, a series coil is inserted only in the input port, and a parallel capacitor is connected to the input end of the series coil. FIG. 9C shows a nonreciprocal circuit device in which parallel capacitors are connected to all ports, and a series coil and a series capacitor are inserted only in the terminating side.
The above conventional nonreciprocal circuit devices have the following problems.
According to the nonreciprocal circuit device in FIG. 8A, a low-loss, small-sized nonreciprocal circuit device can be formed by using a simple matching circuit, but the characteristic impedance thereof is fixed.
According to the nonreciprocal circuit device in FIG. 8B, a nonreciprocal circuit device can be formed which has broad ranges of characteristics in all the ports, such as insertion loss, isolation characteristic, and reflection loss, but an increased number of components increases the device size and cost, and a loss in each port increases.
According to the nonreciprocal circuit device in FIG. 8C, a nonreciprocal circuit device can be formed in which a characteristic impedance can be arbitrarily set in each port, but an increased number of components increases the loss of each port. When the circuit is formed so as to have a predetermined input impedance caused by a low resistance and to set the output impedance at 50 ohms, the exterior dimensions of the series capacitor in the output port increase. Specifically, for example, when the input impedance is 12 ohms and the output impedance is 50 ohms, the capacitances of the capacitors are as follows: the input-port series capacitor is 7 pF, the input-port parallel capacitor is 3 pF, the output-port series capacitor is 50 pF, and the 20 output-port parallel capacitor is 12 pF.
Accordingly, a capacitor having a large exterior size must be used as the output-port capacitor, so it is difficult to built the capacitor into the nonreciprocal circuit device. Also, when a laminated capacitor is used for size reduction, a new problem occurs in that the insertion loss increases because the Q value decreases in the microwave bands above about 1 GHz. For example, the Q value in the 1-GHz band of a laminated capacitor having 50 pF is approximately 10, so that an insertion loss of approximately 0.05 dB occurs.
In a case in which the nonreciprocal circuit device is used for connecting a circuit to an antenna, which is a main use of the nonreciprocal circuit device, there is a possibility that, because lightning can cause a large amount of static electricity to be stored in the series capacitor and parallel capacitor of the output port, the stored charge can exceed a withstand amount so as to heat and destroy the capacitor, or even components of the circuit. To prevent this problem, a resistor, an RF choke coil, or a surge absorber may be connected between the output terminal and the ground terminal. However, the loss and cost will increase, and size reduction becomes difficult.
In addition, in the process of producing a nonreciprocal circuit device, in general, the high frequency characteristics of the central conductor, the input and output terminals, and the ground terminal are inspected. Since measurement thereof takes a long time, in a pre-process before the inspection, the state of connection between the central conductor and the input and output terminals is inspected by using direct-current conduction. However, when the series capacitor is inserted between the central conductor and the input and output terminals, open-state detection by direct-current conduction cannot be performed, so that all nonreciprocal circuits must be inspected concerning high frequency characteristics. This increases the number of steps of production and the cost.
While the high frequency characteristic inspection is being performed, the central conductor is pressed onto the input and output terminal and the ground terminal. The pressure may warp the housing so that the respective portion between the central conductor and each terminal, which must be originally open, can be unstably connected, and the nonreciprocal circuit device may require further processing. Originally, the open state can be detected by the connection-state inspection using direct-current conduction. However, as described above, according to the nonreciprocal circuit device in FIG. 8C, it is difficult to prevent a defective product from being distributed since a series capacitor is inserted in each port.
The nonreciprocal circuit device in FIG. 9A attenuates a signal outside the targeted band because the input port has a broad range of reflection loss characteristics. However, since the coil is used, a magnetic path for preventing the deterioration of the Q value is separately required.
The nonreciprocal circuit device in FIG. 9B attenuates an unnecessary signal outside the targeted band (particularly on the high-frequency side). However, the device is enlarged since it has coils.
According to the nonreciprocal circuit device in FIG. 9C, a nonreciprocal circuit device can be formed which has a broad range of isolation characteristic despite low loss. However, the device is enlarged since it has coils.
The present invention provides a small-sized nonreciprocal circuit device in which an arbitrary input impedance can be set, in which matching to an arbitrary value of a terminating resistor can be performed, and which has a low loss in the entirety of the device. The invention also provides a communication apparatus provided with the nonreciprocal circuit device.
To this end, according to an aspect of the present invention, there is provided a nonreciprocal circuit device including a ferrite member, a central conductor having an input port, an output port, and a terminating port wherein the input port, the output port, the terminating port cross on the ferrite member, a permanent magnet applying a static magnetic field to the ferrite member and the central conductor, an input terminal and an output terminal for inputting and outputting a signal, and a ground terminal functioning as the ground. The nonreciprocal circuit device further includes a parallel capacitor connected between the output port and the ground terminal, a parallel capacitor connected between the terminating port and the ground terminal, a series capacitor connected between the input port and the input terminal, and a parallel capacitor connected between the input terminal and the ground terminal.
According to another aspect of the present invention, there is provided a nonreciprocal circuit device including a ferrite member, a central conductor having an input port, an output port, and a terminating port wherein the input port, the output port, the terminating port cross on the ferrite member, a permanent magnet applying a static magnetic field to the ferrite member and the central conductor, an input terminal and an output terminal for inputting and outputting a signal, a ground terminal functioning as the ground, and a terminating resistor connected to the terminating port. The nonreciprocal circuit device further includes a parallel capacitor connected between the output port and the ground terminal, a series capacitor connected between the input port and the input terminal, a parallel capacitor connected between the input terminal and the ground terminal, and a series capacitor connected between the terminating port and the terminating resistor.
Preferably, the nonreciprocal circuit device further includes a parallel capacitor connected between the terminating resistor and the ground terminal.
According to another aspect of the present invention, there is provided a nonreciprocal circuit device including a ferrite member, a central conductor having an input port, an output port, and a terminating port wherein the input port, the output port, the terminating port cross on the ferrite member, a permanent magnet applying a static magnetic field to the ferrite member and the central conductor, an input terminal and an output terminal for inputting and outputting a signal, and a ground terminal functioning as the ground. The nonreciprocal circuit device further includes a parallel capacitor connected between the output port and the ground terminal, a parallel capacitor connected between the terminating port and the ground terminal, a series capacitor connected between the input port and the input terminal, and a parallel capacitor connected between the input port and the ground terminal.
Preferably, the input port is disposed between the parallel capacitor and the series capacitor which are both connected to the input port. Also preferably, the input port is connected to a connection point defined between the parallel capacitor and the series capacitor which are both connected to the input port.
The parallel capacitor and the series capacitor may be single-substrate capacitors.
The input impedance of the input port may be in a range of 3 to 45 ohms.
The resistance of the terminating resistor may be in a range of 3 to 360 ohms.
According to another aspect of the present invention, there is provided a communication apparatus including one of the above nonreciprocal circuit devices.
According to the present invention, by employing a structure in which a parallel capacitor is connected between a ground terminal and each port of a central conductor and a series capacitor is inserted in an input port, a low-loss, small-sized nonreciprocal circuit device in which an input impedance can be arbitrarily selected can be inexpensively formed.
According to the present invention, by employing a structure in which a series capacitor is inserted in an input port, breakage of a circuit component by the inflow of static electricity from the outside via an output terminal can be prevented, and connection-state inspection using direct current conduction of the output terminal can be performed.
According to the present invention, a series capacitor is inserted in the input port of a central conductor, so that a direct-current component which flows in a nonreciprocal circuit device is excluded and an additional circuit for excluding the direct-current component is not required. This makes it possible to form an inexpensive, low-loss nonreciprocal circuit device.
According to the present invention, by employing a structure in which a series capacitor is inserted in the terminating port, a nonreciprocal circuit device in which an arbitrary value of a terminating resistor can be set can be formed.
According to the present invention, by employing a structure in which a parallel capacitor and a series capacitor which are connected to an input port are provided with the input port provided therebetween, a small-sized nonreciprocal circuit device can be formed.
According to the present invention, by using a single-substrate capacitor to form each capacitor, a low-loss, small sized nonreciprocal circuit device can be formed.
According to the present invention, by employing a structure in which an input impedance is set to 3 to 45 ohms, a nonreciprocal circuit device can be formed which has a low loss even when a circuit component required to have a load of low impedance is connected to the nonreciprocal circuit device.
According to the present invention, by employing a structure in which the resistance of a terminating resistor is to 3 to 360 ohms, a terminating resistor having a small number of parasitic components can be formed, and an inexpensive low-loss nonreciprocal circuit device can be formed.
According to the present invention, by employing a structure including one of the above nonreciprocal circuit devices, a small-sized communication apparatus having high communication performance can be inexpensively obtained.
Other features and advantages of the invention will be appreciated from the following detailed description of embodiments thereof, with reference to the drawings, in whidh like references denote like elements and parts.